Quartz tube electric heaters are well known in the art and usually comprise a quartz tube in which a heater wire is suspended. In an effort to obtain greater heat output, these heater wires are sometimes formed as helical coils which are suspended in the tube. However, at the high temperatures at which these heaters operate, the resistance wires suffer a reduction in stiffness and the unsupported turns of the helix tend to collapse, losing their symmetry, which causes "hot spots" in the wire and further loss of symmetry, until a burn-out of the coil occurs.
Another disadvantage of conventional quartz tube heaters is that they radiate heat over 360.degree., when a more limited area of radiation is usually desired. In an effort to overcome this drawback, external reflectors are positioned around a portion of the circumference of the quartz tube, but these reflectors usually become tarnished and dirty, losing their efficiency.
A good example of efforts to overcome these disadvantages can be seen in U.S. Pat. No. 3,699,309, in which a coil is disposed within a quartz tube between a reflective body therein and the inner surface of the tube, the reflective body having a planar surface.
The disadvantage of this example is that the coil is only supported at two diametrically opposite points of the turns thereof, so that the coil can still collapse between these points, becoming elliptical instead of circular, while the planar reflective surface gives a radiation spread of no less than 180.degree., which for most applications is still too wide.
A still further disadvantage of the known quartz tube heaters is the fact that the tubes are mechanically mounted within the heater housing, so that if a burn-out of the quartz tube occurs, which is more likely in these types of heaters, removal of the heater is awkward and time consuming.